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Subject Re: sandbox/messaging - your feedbacks are welcome
Date Wed, 21 Jul 2004 07:28:53 GMT
For clustering, we've been working quite heavily for some time on this 

(Note that ActiveCluster is not Geronimo specific and so can be used to 
build clusters or anything).

The current implementation works on top of any JMS provider, such as 
ActiveMQ, which can work over UDP, multicast, TCP, SSL, g-network, 
JGroups, JXTA etc.

Jules has been working hard on distributed session state and handling 
fail-over gracefully and cluster wide topology organisation protocols 
such as for arranging buddies over subnets / DR zones and the like 
using WADI

which is using ActiveCluster and Jules is starting to put together 
various algorithms for choosing buddies, pairs, sub-nets, controllers 
and the like.

Notice the simpler API for ActiveCluster which just reuses a few 
interfaces from JMS.

It seems your new messaging.cluster API is pretty similar to 
ActiveCluster. Any ideas why you didn't just use ActiveCluster? 
(Especially as I mentioned it to you quite a while ago :)

Also, as I said to you a while ago, I don't see why the messaging 
package doesn't use the JMS API for things like Msg / MsgBody / 
MsgConsumer / MsgProducer and so forth. Not only would this mean your 
API would become more J2EE standard, it'd mean you could reuse heaps of 
open source and commercial implementations.

On 20 Jul 2004, at 05:07, Gianny Damour wrote:

> Hello,
> I am working on a prototype, sandbox/messaging, focused on providing 
> the infrastructure for the implementation of clustered applications. 
> This proto has reached a stage, which is according to me "good enough" 
> for judgment.
> I will try to describe here the main features of this infrastructure; 
> hence, this memo will be a little bit long.
> Its core ideas are:
> - to provide a mechanism to cluster/inter-connect N Geronimo servers. 
> The way these servers are inter-connected should be at the same time 
> manageable (e.g. I want this server to be connected to this one) and 
> to some extent automatic (e.g. when a new server is detected, it 
> should be added automatically to the cluster); and
> - to provide a set of base services built on top of the above 
> infrastructure to simplify the implementation of clustered 
> applications (e.g. creation of proxies for services running on remote 
> Geronimo server).
> Let's talk in more details about the way Geronimo servers are 
> clustered. The implementation achieve this goal by organizing servers 
> in a known and configurable topology, e.g. star, ring, hyper-cube, 
> where edges of the associated graphs represent connections. At the 
> very beginning, a server and two heartbeat services, namely heartbeat 
> sender and heartbeat monitor, are started. The heartbeat sender sends 
> periodically an heartbeat consisting of the meta-data (IP address, 
> port and name) of its associated server to a multicast group. The 
> heartbeat monitor monitors these heartbeats and detects the 
> availability or failure of servers. When a new server is available or 
> a failure is detected, a new topology is computed and cascaded to the 
> servers of the current topology.
> Let's consider the following scenario:
> Geronimo servers are organized in a ring topology; four servers are 
> started and one server is killed.
> 1. starts the first server, namely LearderNode. As it is the first 
> server, it is in a stand-alone mode;
> 2. starts the second server, namely Node1. This server is detected by 
> LeaderNode, which triggers a reconfiguration. The topology is 
> LeaderNode -- Node1 -- LeaderNode;
> 3. starts the third server, namely Node2. LeaderNode inserts Node2 
> between itself and Node1. The topology is LeaderNode -- Node1 -- Node2 
> -- LeaderNode;
> 4. starts a fourth server, namely Node3. Detected by LeaderNode, it 
> inserts Node3 between itself and Node2. The topology is LeaderNode -- 
> Node1 -- Node2 -- Node3 -- LeaderNode; and
> 5. stops Node2. LeaderNode drops it from the ring. The topology is 
> LeaderNode -- Node1 -- Node3 -- LeaderNode.
> As the proto supports the ring topology, it is possible to trial this 
> scenario:
> cd sandbox/messaging
> maven (ClusterHBTest may fail, so ignore the test failures if required)
> maven -patch
> cd ../..
> java -jar target/bin/server.jar org/apache/geronimo/LeaderCluster
> java -jar target/bin/server-1101.jar org/apache/geronimo/Cluster8091
> java -jar target/bin/server-1102.jar org/apache/geronimo/Cluster8092
> java -jar target/bin/server-1103.jar org/apache/geronimo/Cluster8093
> kill <the process java -jar target/bin/server-1102.jar 
> org/apache/geronimo/Cluster8092>
> As a conclusion, this prototype tries to federate Geronimo servers in 
> specific topologies. As an aside, it is rather simple to support other 
> kinds of topologies without significant efforts. For instance, one of 
> the JUnit test (NodeImplTest)  uses a bus topology.
> Based on the knowledge of the enforced topology,  it should be 
> possible to implement "efficient" clustered applications. For 
> instance, the replication of Web sessions could work as follow: 
> replicate the sessions created on this server to all of its direct 
> neighbours (neighbours can be easily retrieved via a topology). This 
> way the load is evenly distributed as long as sessions are evenly 
> created in the cluster.
> On top of this infrastructure, the proto implements a set of basic 
> services, which could simplify the implementation of such clustered 
> applications. These services are:
> - customization of the marshalling/unmarshalling of Objects to be 
> sent/received to/from a remote server: it is possible to replace 
> specific objects;
> - InputStream can be passed between servers: by leveraging the 
> previous feature, InputStreams are replaced by a proxy which can be 
> used to pull the content of an InputStream hosted on a remote server. 
> This can be useful when dumping the content of a server to another 
> server in order to initialize its state;
> - primitive reference layer: Objects implementing a specific interface 
> can be passed around even if not serializable. For instance, the 
> current implementation can pass around a MBeanServer (this is a bad 
> example as JSR 160 is intended for that). If you have a look to 
> MBeanServerEndPointImpl, you will see that this is actually the 
> ability to return by reference an object to the remote caller. As this 
> caller can also provide parameters, which implements this specific 
> interface, one can achieves a pass by reference for both the 
> parameters and the result between two servers;
> - proxy creation: it is the ability to acquire a proxy for a service 
> running on a remote server:
> // Defines the proxy meta-data.
>            EndPointProxyInfo proxyInfo = new EndPointProxyInfo(
>                NodeEndPointView.NODE_ID, NodeEndPointView.class, 
> nodeInfo);
> // Builds the proxy.
>            NodeEndPointView topologyEndPoint =
>                (NodeEndPointView) 
> endPointProxyFactory.factory(proxyInfo);
> // Transforms the Msgs which will be sent by this proxy.
>            ((EndPointProxy) topologyEndPoint).setTransformer(new 
> MsgTransformer() {...});
> // This call will actually invoke the service on the server nodeInfo.
>                topologyEndPoint.prepareTopology(aTopology);
> As an aside, whatever the number of services communication with other 
> remote services, the number of connections stay low: it is the number 
> of edges defined by the current topology.
> This proto has some bugs (e.g. memory leak of the reference layer) and 
> some enhancements are required (e.g. classloading strategy is to be 
> added). Nevertheless, I would like to have your inputs about the 
> general concept and the current state of the implementation prior to 
> progress any further.
> Cheers,
> Gianny


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